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filterWithKey

Note

This is a point-in-time snapshot of the API documentation from January 2026. Going forward, we will not be maintaining a public copy of these references, and recommend users to refer to the built-in signature helpers available in the Hack LSP instead for complete and up-to-date information.

Returns a MutableMap containing the values of the current MutableMap that meet a supplied condition applied to its keys and values

public function filterWithKey(
  (function(Tk, Tv): bool) $fn,
): MutableMap<Tk, Tv>;

Only keys and values that meet a certain criteria are affected by a call to filterWithKey(), while all values are affected by a call to mapWithKey().

The keys associated with the current MutableMap remain unchanged in the returned MutableMap; the keys will be used in the filtering process only.

Parameters​

  • (function(Tk, Tv): bool) $fn - The callback containing the condition to apply to the current MutableMap keys and values.

Returns​